Mechanisms and Kinetics of Reactions of the O (1D,3p) + CF3Cl System

In the stratosphere, CF3Cl (CFC 13) can either photodecompose or react directly with atomic oxygen to generate ozone-depleting agents such as Cl and ClO in the gas phase[1-3]. Since the 1970s, attention has been focused on the effects of these compounds on the destruction of ozone in the stratosphere and on global warming[4,5].     

Characterisation of Some Phytochemicals Extracted from Black Elder (Sambucus nigra L.) Flowers Subjected to Ozone Treatment

Elderflowers are a well-known source of bioactive compounds. The amount of isolated bioactive compounds may be increased by applying various abiotic and biotic factors. Gaseous ozone (10 and 100 ppm) was used in the process of preparing flowers. Next, the flowers were treated with sugar syrup to extract bioactive compounds. It was shown that this treatment, including the influence of extraction temperature, significantly affects the contents of polyphenols (liquid chromatography–mass spectrometry (LC–MS) methods) and vitamin C, as well as the antioxidant potential (cupric reducing antioxidant capacity (CUPRAC method)), the profile of volatile substances (head space–solid-phase microextraction (HS–SPME methods)) and the colour of the syrup (Commission Internationale de l’Eclairage (CIE) L*a*b* methods). The findings show that an increased dose of ozone and higher extraction temperature applied in the process of syrup production resulted in higher contents and different compositions of bioactive compounds. The highest contents of bioactive compounds were identified in syrup obtained from raw material treated with ozone for 15 min (concentration = 10 ppm) and extraction with sugar syrup at a temperature of 60 °C.     

Fluorocarbons in the global environment: a review of the important interactions with atmospheric chemistry and physics

Fluorocarbon impact on ozone depletion is reviewed together with the efficacy of the Montreal Protocol in acting to correct the imbalance between stratospheric ozone production and destruction. The Protocol is also helping to reduce global warming: CFCs are shown to be currently the largest fluorocarbon contributors to climate change. Relative contributions to climate change from CFCs and their HFC substitutes are discussed, together with the consequences of control of minor greenhouse gases on an environmental impact which is dominated by carbon dioxide emissions. Both the potencies of the materials for environmental change and their concentrations in the atmosphere are important and are considered here.Trifluoroacetic acid, a minor product of atmospheric decomposition of some HCFCs and HFCs and of the pyrolysis of fluoropolymers, has been shown to be uniformly distributed in seawater to a depth of over 4000 m and so is natural, although the actual source has yet to be identified.The Montreal Protocol is only one example of action to reduce undesirable impact from fluorocarbons. Other, less universal, actions include abatement of fluoroform greenhouse gas emissions from HCFC manufacturing, process changes to eliminate trifluoromethylsulfur pentafluoride emissions from electrochemical fluorination and ceasing manufacture of perfluorooctanyl sulfonate compounds due to their persistence in human tissue.     

The lifetime of CFC substitutes studied by a network trained with chaotic mapping modified genetic algorithm and DFT calculations

The hydrohaloalkanes have attracted much attention as potential substitutes of chlorofluorocarbons (CFCs) that deplete the ozone layer and lead to great high global warming. Having a short atmospheric lifetime is very important for the potential substitutes that may also induce ozone depletion and yield high global warming gases to be put in use. Quantitative structure-activity relationship (QSAR) studies were presented for their lifetimes aided by the quantum chemistry parameters including net charges, Mulliken overlaps, E(HOMO) and E(LUMO) based on the density functional theory (DFT) at B3PW91 level, and the C-H bond dissociation energy based on AM1 calculations. Outstanding features of the logistic mapping, a simple chaotic system, especially the inherent ability to search the space of interest exhaustively have been utilized. The chaotic mapping aided genetic algorithm artificial neural network training scheme (CGANN) showed better performance than the conventional genetic algorithm ANN training when the structure of the data set was not favorable. The lifetimes of HFCs and HCs appeared to be greatly dependent on their energies of the highest occupied molecular orbitals. The perference of the RMSRE comparing to RMSE as objective function of ANN training was better for the samples of interest with relatively short lifetimes. C(2)H(6) and C(3)H(8) as potential green substitutes of CFCs present relatively short lifetimes.     

Structures and Properties of trans-1,3,3,3-Tetrafluoro- propene (HFO-1234ze) and 2,3,3,3-Tetrafluoropropene (HFO-1234yf) Refrigerants

The refrigerant trans-1,3,3,3-tetrafluoropropene (HFO-1234ze) is used as a replacement for former cooling agents that have been phased-out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO-1234ze are known. We report structure determinations based on low-temperature single-crystal X-ray diffraction data as well as gas-phase diffraction data of HFO-1234ze and HFO-1234yf (2,3,3,3-tetrafluoropropene). Furthermore, vibrational spectra of HFO-1234ze in all phases are described. The results are discussed together with quantum-chemical calculations on the PBE0/cc-pVTZ level of theory. Combustion experiments of HFO-1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products.     

Ozonolysis of geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal: kinetics and mechanisms

A combined density functional theory and transition-state theory study of the mechanisms and reaction coefficients of gas-phase ozonolysis of geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal is presented. The geometries, energies, and harmonic vibrational frequencies of each stationary point were determined by B3LYP/6-31(d,p), MPW1K/cc-pVDZ, and BH&HLYP/cc-pVDZ methods. According to the calculations, the ozone 6-methyl-5-hepten-2-one reaction is faster than the ozone 6-hydroxy-4-methyl-4-hexenal reaction, but both are slower than the ozone geraniol-trans reaction. By using the BH&HLYP/cc-pVDZ data, a global rate coefficient of 5.9 x 10(-16) cm(3) molecule(-1) s(-1) was calculated, corresponding to the sum of geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal reactions with the ozone. These results are in good agreement with the experimental studies.     

An overview of commonly used semiconductor nanoparticles in photocatalysis

The depletion of non-renewable resources and rise in global warming has caused great concern to humankind. With a view to use renewable source of energy and to eliminate hazardous chemical compounds from air, soil, and water, photocatalysis utilizing solar energy is becoming a rapidly expanding technology. Semiconductor nanoparticles have the ability to undergo photoinduced electron transfer to an adsorbed particle governed by the band energy positions of the semiconductor and the redox potential of the adsorbate. A brief overview of metal oxides and sulphides that can act as sensitizers for light-induced redox processes due to their electronic structure is presented here.     

The lifetime of CFC substitutes studied by a network trained with chaotic mapping modified genetic algorithm and DFT calculations

The hydrohaloalkanes have attracted much attention as potential substitutes of chlorofluorocarbons (CFCs) that deplete the ozone layer and lead to great high global warming. Having a short atmospheric lifetime is very important for the potential substitutes that may also induce ozone depletion and yield high global warming gases to be put in use. Quantitative structure–activity relationship (QSAR) studies were presented for their lifetimes aided by the quantum chemistry parameters including net charges, Mulliken overlaps, E _HOMO and E _LUMO based on the density functional theory (DFT) at B3PW91 level, and the C-H bond dissociation energy based on AM1 calculations. Outstanding features of the logistic mapping, a simple chaotic system, especially the inherent ability to search the space of interest exhaustively have been utilized. The chaotic mapping aided genetic algorithm artificial neural network training scheme (CGANN) showed better performance than the conventional genetic algorithm ANN training when the structure of the data set was not favorable. The lifetimes of HFCs and HCs appeared to be greatly dependent on their energies of the highest occupied molecular orbitals. The perference of the RMSRE comparing to RMSE as objective function of ANN training was better for the samples of interest with relatively short lifetimes. C₂H₆ and C₃H₈ as potential green substitutes of CFCs present relatively short lifetimes.     

A NUMERICAL EXPERIMENT FOR EFFECTS OF OZONE HEATING ON GENERAL CIRCULATION

An ozone conservation equation is added to the global nine-layer general circulationmodel to simulate the heating effect on the upper atmosphere due to the absorption of theultraviolet part of solar radiation by ozone and the changes of temperature, pressure andwind fields caused by ozone heating. The experiment shows that the heating rate by ozoneis much larger than that by other elements such as water vapour in stratosphere. Thetemperature distribution and strength of zonal wind in tropopause and above calculated withozone effect are much different from the results simulated without ozone. The ozone heatingaffects not only the zonal wind but also the meridional wind, so that the Walker Circulationand Hadley Cell are all changed accordingly. Besides, it can be seen that the influences ofozone on the meteorological elements are small in troposphere, while it still makes apparentlyresponse near the surface. Especially, it is much larger above the land than above the ocean.     

Contribution to Global Warming of Plasma Polymerization and Treatment Processes Fed with Fluorinated Compounds

Many fluorine containing compounds utilized in plasma processing, namely plasma polymerization and treatment of materials, have marked greenhouse characteristics as they are able to absorb IR-radiation and have long lifetimes in the atmosphere. The unreacted portion of the feeds and some by-products released in the atmosphere during plasma processing contribute to the global warming of the Earth. This is a problem whose general aspects are discussed in this paper, together with the evaluation of the effects on global warming of the effluents of plasmas fed with some fluorine containing compounds.     

光催化CO2转化为碳氢燃料体系的综述

传统化石能源燃烧产生CO₂引起的地球变暖和能源短缺已经成为一个严重的全球性问题. 利用太阳光和光催化材料将CO₂还原为碳氢燃料, 不仅可以减少空气中CO₂浓度, 降低温室效应的影响, 还可以提供碳氢燃料, 缓解能源短缺问题, 因此日益受到各国科学家的高度关注. 本文综述了光催化还原CO₂为碳氢燃料的研究进展, 介绍了光催化还原CO₂的反应机理, 并对现阶段报道的光催化还原CO₂材料体系进行了整理和分类, 包括TiO₂光催化材料, ABO₃型钙钛矿光催化材料, 尖晶石型光催化材料, 掺杂型光催化材料, 复合光催化材料, V、W、Ge、Ga基光催化材料及石墨烯基光催化材料. 评述了各种材料体系的特点及光催化性能的一些影响因素. 最后对光催化还原CO₂的研究前景进行了展望.     

Mechanism,kinetics, and environmental assessment of OH-initiated transformation of CTDE in the atmosphere

The transformation mechanism and kinetics of 2-chloro-1,1,2-trifluoroethyl-difluoromethyl-ether (CTDE, CHF₂OCF₂CHFCl) triggered by OH radicals are studied by density-functional theory methods and canonical variational transition state theory. The computational rate constant including small-curvature tunneling correction is found to be in commendable agreement with the experimental data. Two hydrogen abstraction channels to form the alkyl radicals of C·F₂OCF₂CHFCl and CHF₂OCF₂C·FCl are observed, and the formation of CHF₂OCF₂C·FCl is found to be more favorable than C·F₂OCF₂CHFCl kinetically and thermodynamically. Subsequent evolution of CHF₂OCF₂C·FCl in the presence of NO and O₂ indicates that the organic nitrate (CHF₂OCF₂CONO₂FCl) is the stable product. The dechlorinate of alkoxy radical (CHF₂OCF₂C(O·)FCl) is the most favorable degradation channel, and the estimated ozone depletion potential for CTDE relative to chlorofluorocarbon-11 is 0.0204, which could lead to ozone depletion as a consequence. The computed atmospheric lifetime for CTDE is found to be 3.69 years by considering the combined contributions from OH radicals and Cl atoms. The total radiative forcing and global warming potential of CTDE are, respectively, 0.547 W m⁻² ppbv and 628.58 (100 years) at 298 K, suggesting that the contribution of CTDE to the greenhouse effect is moderate.     

Surface Modification of (001) Facets Dominated TiO2 with Ozone for Adsorption and Photocatalytic Degradation of Gaseous Toluene

This study investigated the positive effect of surface modification with ozone on the photocatalytic performance of anatase TiO₂ with dominated (001) facets for toluene degradation. The performance of photocatalyst was tested on a home-made volatile organic compounds degradation system. The ozone modi cation, toluene adsorption and degradation mechanism were established by a combination of various characterization methods, in situ diffuse reflectance infrared fourier transform spectroscopy, and density functional theory calculation. The surface modi cation with ozone can significantly enhance the photocatalytic degradation performance for toluene. The abundant unsaturated coordinated 5c-Ti sites on (001) facets act as the adsorption sites for ozone. The formed Ti-O bonds reacted with H₂O to generate a large amount of isolated Ti_5c-OH which act as the adsorption sites for toluene, and thus significantly increase the adsorption capacity for toluene. The outstanding photocatalytic performance of ozone-modified TiO₂ is due to its high adsorption ability for toluene and the abundant surface hydroxyl groups, which produce very reactive OH radicals under irradiation. Furthermore, the O₂ generated via ozone dissociation could combine with the photogenerated electrons to form superoxide radicals which are also conductive to the toluene degradation.     

Thermal analyses of home-made zeolite by DSC and TG

Volatile organic compounds (VOCs) and greenhouse gases are the main factors involved in pollution control and global warming. Various treatment methods involving incineration, adsorption, etc., have been employed to reduce VOCs and greenhouse gases concentration in the operating environment and atmosphere. Activated carbon, zeolite, silica gel, and alumina have been broadly used to adsorb pollutants in various industrial applications. Based on the promising effect of adsorption, we analyzed and identified the thermal phenomena of home-made zeolite using various instruments. The endothermic reaction under 100?°C of home-made zeolite was identified as steam adsorption, which is an important discovery. The optimal adsorption temperatures of home-made zeolite have been determined at 200?C550?°C.     

Comparison of analytical methods for ozone precursors using adsorption tube and canister

Recently, ozone concentrations have increased dramatically as a result of vehicle usage in metropolitan areas. Ozone precursors are composed of hydrocarbons of organic compounds. Because hydrocarbons are indicative of ozone formation, they need to be monitored in ambient air. Since ozone precursor are present at very low levels (from ppb to ppt) in ambient air, they are difficult to analyze accurately. This study investigates ozone precursors in ambient air. The main purpose of this study is to compare analytical methods for the measurement of ozone precursors in atmosphere. Two measurement methods were evaluated using canister (Silco-canister) and adsorbent (300-mg Carbopack B+150-mg Carbosieve SIII) tube. Differences in measurements for total ozone precursor emissions were 54.1% between the adsorption tube and canister-GC/MS, 51.1% between adsorption tube and canister-GC/FID, and 16.3% between canister-GC/MS and canister-GC/FID.     

Electrosynthesis of cyclic carbonates from epoxides and atmospheric pressure carbon dioxide

The use of CO(2) for the preparation of value-added compounds has dramatically increased due to increased global warming concerns. We herein report an electrochemical cell containing a copper cathode and a magnesium anode that effectively converts epoxides and carbon dioxide to cyclic carbonates under mild electrochemical conditions at atmospheric pressure.     

Ozone reaction with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol, and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge

Ozone reacts with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge. Destruction of n-aldehydes increases with n number and with ozone concentration. In some sampling experiments both generation and destruction of n-aldehydes by ozone are observed. In field experiments the results of sample analysis for n-aldehydes and benzaldehyde are frequently not proportional to sample volume whereas results for toluene and isoprene, and sometimes for total carbon, are. A simple theory is developed to simulate the net result of three processes: the adsorption of compounds from an air stream onto a solid adsorbent, the generation of compounds by reaction of ozone with materials upstream of or on the adsorbent, and the destruction by ozone of pre-existing compounds and compounds adsorbed from the sample stream. The use of distributed volume pairs is recommended as a way to identify loss of sample integrity during air monitoring experiments.     

Abatement of Tetrafluormethane Using Thermal Steam Plasma

Plasma Chemistry and Plasma Processing - Perfluorinated compounds (PFCs) increasingly utilized in electronic manufacturing represent a potent source of global warming effect. Because of extremely...     

Biological technologies for the treatment of atmospheric pollutants

Most industrial activities emit atmospheric pollutants nowadays. Many of these activities are performed in stationary hotspots such as chemical industry facilities, wastewater and solid waste treatment plants. Other important stationary sources of gas pollutants include facilities for mining, intensive livestock farming and rendering. Volatile organic compounds (VOCs), odours and greenhouse gases are released from the above-mentioned sources, leading to issues related to global warming, health disorders and complaints to public administrations due to odour annoyance. When the release of atmospheric pollutants cannot be prevented, the sort of pollutants, their concentration and the flow rate of the waste gas emission must be characterised in order to select the most cost-effective treatment technology. Over the last decades, the use of biological technologies for the treatment of atmospheric pollutants has gradually increased due to their proven robustness, high cost-effectiveness and low environmental impact. The fundamentals of the most commonly implemented biological technologies in industrial applications (biofiltration, biotrickling filtration, bioscrubbing and activated sludge diffusion) are described in this work. The latest findings in the field of biological technologies for air pollution control are also presented and discussed.